We have continued to work on determining the characteristics of cells in cultures of spinal cord cells from fetal mice. The system may be used to assess toxicity of drugs and other additives on the cells with acute or chronic treatment. The activity of choline acetyltransferase in the cultures was markedly decreased by 2 week treatment of cultures with concentrations of phenobarbital which were within the therapeutic range. This was true whether the cells were treated beginning on the day of plotting or after 1-2 weeks in culture. With both treatment schedules there was also a decrease in the number of large (greater than 22 microns diameter) neurons in the cultures, but no loss of dorsal root ganglion neurons. With 2 weeks recovery after treatment there was return toward normal of neuron number or enzyme activity, and a non-barbiturate anticonvulsant, valproate, did not similarly depress enzyme activities in the cultures.